Image coding method, image decoding method, image coding apparatus, image decoding apparatus, and image coding-decoding apparatus

ABSTRACT

An image coding method includes: generating a predicted block; calculating a residual block; calculating quantized coefficients by performing transform and quantization on the residual block; calculating a coded residual block by performing inverse quantization and inverse transform on the quantized coefficients; generating a temporary coded block; determining whether or not an offset process is required, to generate first flag information indicating a result of the determination; executing the offset process on the temporary coded block when it is determined that the offset process is required; and performing variable-length coding on the quantized coefficients and the first flag information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 13/817,316,which is the National Stage of International Application No.PCT/JP2012/004136, filed Jun. 26, 2012, which claims the benefit of U.S.Provisional Patent Application No. 61/501,384, filed Jun. 27, 2011. Theentire disclosures of the above-identified applications, including thespecification, drawings and claims are incorporated herein by referencein their entirety.

TECHNICAL FIELD

The present invention relates to an image coding method, an imagedecoding method, an image coding apparatus, an image decoding apparatus,and an image coding-decoding apparatus. In particular, the presentinvention relates to an image coding method, an image decoding method,an image coding apparatus, an image decoding apparatus, and an imagecoding-decoding apparatus with less loss in image quality.

BACKGROUND ART

In recent years, the number of applications used for, for example,video-on-demand type service including video-conferencing, digital videobroadcasting, and video content streaming via the Internet isincreasing. These applications are dependent on the transmission ofvideo data. When the video data is transmitted or recorded, asignificant amount of data is transmitted through a conventionaltransmission channel having a limited bandwidth or is recorded into aconventional recording medium having a limited data capacity. In orderto transmit the video data through the conventional transmission channelor record the video data into the conventional recording medium, it isabsolutely essential to compress or reduce the amount of digital data.

With this being the situation, multiple video coding standards have beendeveloped for video data compression. Examples of the video codingstandards include the standards of the International TelecommunicationUnion Telecommunication Standardization Sector (ITU-T) specified by“H.26x” and the International Standards Organization/InternationalElectrotechnical Commission (ISO/IEC) specified by “MPEG-x”. Currently,the latest and most advanced video coding standard is presented by theH.264/AVC or MPEG-4 AVC standard (see Non Patent Literatures 1 and 2).

Moreover, various studies are made to improve the coding efficiency bythe High Efficiency Video Coding (HEVC) standard which is anext-generation image coding standard (see Non Patent Literature 3).

CITATION LIST Non Patent Literature

-   [NPL 1]-   ISO/IEC 14496-10 “MPEG-4 Part 10, Advanced Video Coding”-   [NPL 2]-   Thomas Wiegand et al, “Overview of the H.264/AVC Video Coding    Standard”, IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO    TECHNOLOGY, JULY 2003, PP. 1-1-   [NPL 3]-   Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3    and ISO/IEC JTC1/SC29/WG11 5th Meeting: Geneva, CH,-6-23 March, 2011    JCTVC-E603 Title:WD3: Working Draft 3 of High-Efficiency Video    Coding ver.7    http://phenix.int-evry.fr/jct/doc_end_user/documents/5_Geneva/w    g11/JCTVC-E603-v7.zip

SUMMARY OF INVENTION Technical Problem

In recent years, image quality is required to be improved while thecoding efficiency is maintained.

In view of this, the present invention is conceived to solve theaforementioned conventional problem, and has an object to provide animage coding method and an image decoding method capable of improving acoded image and a decoded image in image quality.

Solution to Problem

The image coding method in an aspect according to the preset inventionis a method of coding an input block included in an image. To be morespecific, the image coding method includes generating a predicted blockby predicting the input block; calculating a residual block bysubtracting the predicted block from the input block; calculatingquantized coefficients by performing transform and quantization on theresidual block; calculating a coded residual block by performing inversequantization and inverse transform on the quantized coefficients;generating a temporary coded block by adding the coded residual block tothe predicted block; determining whether or not an offset process forcorrecting an error included in the temporary coded block is required,to generate first flag information indicating a result of thedetermination, the error being caused by the quantization in thecalculating of quantized coefficients; executing the offset process onthe temporary coded block when it is determined in the determining thatthe offset process is required; and performing variable-length coding onthe quantized coefficients and the first flag information.

It should be noted that a general or specific embodiment in an aspectmay be implemented by a system, a method, an integrated circuit, acomputer program, or a recording medium, or by any combination of asystem, a method, an integrated circuit, a computer program, and arecording medium.

Advantageous Effects of Invention

The present invention can reduce distortion of a chroma signal andimprove subjective image quality.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an example of a configuration of animage coding apparatus in Embodiment 1 according to the presentinvention.

FIG. 2 is a block diagram showing an example of a conventional method ofcoding a chroma signal.

FIG. 3 is a flowchart showing an example of a conventional method ofcoding a chroma signal.

FIG. 4 is a block diagram showing an example of chroma-signal intraprediction in Embodiment 1 according to the present invention.

FIG. 5 is a flowchart showing an example of chroma-signal intraprediction in Embodiment 1 according to the present invention.

FIG. 6 is a schematic diagram showing an example of calculation of achroma-signal intra prediction value, in Embodiment 1 according to thepresent invention.

FIG. 7 is a block diagram showing an example of chroma-signal intraprediction in Embodiment 2 according to the present invention.

FIG. 8 is a flowchart showing an example of chroma-signal intraprediction in Embodiment 2 according to the present invention.

FIG. 9 is a block diagram showing an example of chroma-signal intraprediction in Embodiment 3 according to the present invention.

FIG. 10 is a flowchart showing an example of chroma-signal intraprediction in Embodiment 3 according to the present invention.

FIG. 11A is a schematic diagram showing an example of a unit ofoffsetting used for chroma-signal intra prediction and shows an examplewhere a different offset value is used for each block, in Embodiment 3according to the present invention.

FIG. 11B is a schematic diagram showing an example of a unit ofoffsetting used for chroma-signal intra prediction and shows an examplewhere the same offset value is used in an area A.

FIG. 12 is a block diagram showing an example of a configuration of animage decoding apparatus in Embodiment 4 according to the presentinvention.

FIG. 13 is a block diagram showing an example of a conventional methodof decoding a chroma signal.

FIG. 14 is a flowchart showing an example of a conventional method ofdecoding a chroma signal.

FIG. 15 is a block diagram showing an example of chroma-signal intraprediction in Embodiment 4 according to the present invention.

FIG. 16 is a flowchart showing an example of chroma-signal intraprediction in Embodiment 4 according to the present invention.

FIG. 17 is a block diagram showing an example of chroma-signal intraprediction in Embodiment 5 according to the present invention.

FIG. 18 is a flowchart showing an example of chroma-signal intraprediction in Embodiment 5 according to the present invention.

FIG. 19 is a block diagram showing an example of chroma-signal intraprediction in Embodiment 6 according to the present invention.

FIG. 20 is a flowchart showing an example of chroma-signal intraprediction in Embodiment 6 according to the present invention.

FIG. 21 is a diagram showing a prediction unit syntax which is anexample of chroma-signal intra prediction in Embodiment 4 according tothe present invention.

FIG. 22 is a diagram showing slice data syntax which is an example ofchroma-signal intra prediction in Embodiment 6 according to the presentinvention.

FIG. 23 shows an overall configuration of a content providing system forimplementing content distribution services.

FIG. 24 shows an overall configuration of a digital broadcasting system.

FIG. 25 shows a block diagram illustrating an example of a configurationof a television.

FIG. 26 shows a block diagram illustrating an example of a configurationof an information reproducing/recording unit that reads and writesinformation from and on a recording medium that is an optical disk.

FIG. 27 shows an example of a configuration of a recording medium thatis an optical disk.

FIG. 28A shows an example of a cellular phone.

FIG. 28B is a block diagram showing an example of a configuration of acellular phone.

FIG. 29 illustrates a structure of multiplexed data.

FIG. 30 schematically shows how each stream is multiplexed inmultiplexed data.

FIG. 31 shows how a video stream is stored in a stream of PES packets inmore detail.

FIG. 32 shows a structure of TS packets and source packets in themultiplexed data.

FIG. 33 shows a data structure of a PMT.

FIG. 34 shows an internal structure of multiplexed data information.

FIG. 35 shows an internal structure of stream attribute information.

FIG. 36 shows steps for identifying video data.

FIG. 37 shows an example of a configuration of an integrated circuit forimplementing the moving picture coding method and the moving picturedecoding method according to each of embodiments.

FIG. 38 shows a configuration for switching between driving frequencies.

FIG. 39 shows steps for identifying video data and switching betweendriving frequencies.

FIG. 40 shows an example of a look-up table in which video datastandards are associated with driving frequencies.

FIG. 41A is a diagram showing an example of a configuration for sharinga module of a signal processing unit.

FIG. 41B is a diagram showing another example of a configuration forsharing a module of the signal processing unit.

DESCRIPTION OF EMBODIMENTS [Knowledge Forming Basis of PresentInvention]

As shown in FIG. 1 and FIG. 12 for example, HEVC mainly includesprocesses such as prediction, transform, quantization, and entropycoding. Among these, prediction in turn includes inter frame predictionand intra prediction. Intra prediction is a process where a predictedpixel is generated by interpolation from neighboring pixels inneighboring macroblocks located, for example, above and on the left of acurrent macroblock to be processed and a difference from the predictedpixel is coded. Intra prediction according to the HEVC standard makesprediction at a pixel level instead of a discrete cosine transform (DCT)coefficient level, and also uses pixel prediction patterns in vertical,horizontal, and diagonal directions.

Conventional intra prediction of a chroma signal is described, withreference to FIG. 2, FIG. 3, FIG. 13, and FIG. 14.

A configuration of a chroma-signal intra prediction unit 100 thatperforms chroma-signal intra prediction according to a conventionalimage coding method is described. FIG. 2 is a block diagram showing anexample of the conventional chroma-signal intra prediction unit 100.

As shown in FIG. 2, the chroma-signal intra prediction unit 100 includesan intra-predicted chroma-signal generation unit 110, a residual signalcalculation unit 120, a transform-quantization unit 130, an inversequantization-transform unit 135, a coded-signal generation unit 140, anda coding unit 150.

An operation performed by the conventional chroma-signal intraprediction unit 100 is described in more detail. FIG. 3 is a flowchartshowing a process performed by the chroma-signal intra prediction unit100.

Firstly, the intra-predicted chroma-signal generation unit 110 generatesan intra-predicted chroma signal based on an intra prediction mode, andoutputs the generated signal to the residual signal calculation unit 120and the coded-signal generation unit 140 (Step S1001). The intraprediction mode is indicated as an index number assigned to a method ofgenerating an intra-predicted chroma signal. The intra-predicted chromasignal is generated according to the intra prediction mode using, asappropriate, a coded luma signal of a neighboring block, a coded chromasignal of a neighboring block, and a coded luma signal of the currentblock to be processed.

Next, the residual signal calculation unit 120 calculates a residualsignal from an input chroma signal and the intra-predicted chromasignal, and outputs the residual signal to the transform-quantizationunit 130 (Step S1002). The residual signal is obtained by calculating adifference between the input chroma signal and the intra-predictedchroma signal.

Next, the transform-quantization unit 130 calculates quantizedcoefficients by performing transform and quantization on the residualsignal, and outputs the quantized coefficients to the inversequantization-transform unit 135 and the coding unit 150 (Step S1003).Here, transform refers to a process of transforming the residual signalin a space domain into coefficients in a frequency domain. Byquantization, the coefficient value in the frequency domain obtained bytransforming the residual signal is approximated more roughly. A valueindicating the roughness is referred to as a quantization parameter (mayalso be referred to as the QP hereafter). When the QP is greater,rougher approximation is performed, meaning that an error (aquantization error) is greater between the original input chroma signaland the coded chroma signal described later.

Next, the inverse quantization-transform unit 135 calculates a codedresidual signal by performing inverse quantization and inverse transformon the quantized coefficients, and outputs the coded residual signal tothe coded-signal generation unit 140 (Step S1004). Inverse quantizationand inverse transform are performed by a procedure exactly opposite tothe procedure in Step S1003.

After this, the coded-signal generation unit 140 generates a codedchroma signal from the coded residual signal and the intra-predictedchroma signal (Step S1005). The coded-signal generation unit 140 storesthe generated coded chroma signal into a memory that is not illustratedin the diagram. The coded chroma signal stored into the memory is used,as a coded signal of a neighboring block, by the intra-predictedchroma-signal generation unit 110 in order to generate anintra-predicted chroma signal. The same holds true for a coded lumasignal (an explanation thereof is omitted). The coded chroma signal iscalculated by adding the coded residual signal to the intra-predictedchroma signal.

Next, the coding unit 150 generates a bitstream by coding the quantizedcoefficients and the intra prediction mode (Step S1006). In coding, avariable code is assigned to the quantized coefficients in order for thebit length to be short and, as a result, the compression efficiency isimproved. The bitstream obtained by the efficient data compression istransferred or recorded.

A configuration of a chroma-signal intra prediction unit 300 thatperforms chroma-signal intra prediction according to a conventionalimage decoding method is described. FIG. 13 is a block diagram showingan example of the conventional chroma-signal intra prediction unit 300.

As shown in FIG. 13, the chroma-signal intra prediction unit 300includes a variable-length decoding unit 310, a residual signalobtainment unit 320, an intra-predicted chroma-signal generation unit330, and a decoded-chroma-signal generation unit 340.

An operation performed by the conventional chroma-signal intraprediction unit 300 is described in more detail, with reference to FIG.14. FIG. 14 is a flowchart showing a process performed by thechroma-signal intra prediction unit 300.

Firstly, the chroma-signal intra prediction unit 300 obtains quantizedcoefficients and an intra prediction mode by performing variable-lengthdecoding on the bitstream, and outputs the quantized coefficients andthe intra prediction mode to the residual signal obtainment unit 320 andthe intra-predicted chroma-signal generation unit 330 (Step S3001).

Next, the residual signal obtainment unit 320 obtains a decoded residualsignal by performing inverse quantization and inverse transform on thequantized coefficients, and outputs the decoded residual signal to thedecoded-chroma-signal generation unit 340 (Step S3002). The decodedresidual signal has been approximated more roughly by the quantizationat the time of coding. On account of this, when the decoded chromasignal is generated using this residual signal, an error with respect tothe original input image is caused.

Next, the intra-predicted chroma-signal generation unit 330 generates anintra-predicted chroma signal based on the intra prediction mode, andoutputs the intra-predicted chroma signal to the decoded-chroma-signalgeneration unit 340 (Step S3003). The intra-predicted chroma signal isgenerated according to the intra prediction mode using, as appropriate,a decoded luma signal of a neighboring block, a decoded chroma signal ofa neighboring block, and a decoded luma signal of the current block tobe processed.

Next, the decoded-chroma-signal generation unit 340 generates a decodedchroma signal from the decoded residual signal and the intra-predictedchroma signal (Step S3004). The decoded chroma signal is calculated byadding the decoded residual signal to the intra-predicted chroma signal.The decoded chroma signal generated by the decoded-chroma-signalgeneration unit 340 is stored into a memory, which is not illustrated inthe diagram, and is used for a later intra prediction process, forexample.

According to the aforementioned conventional technology, however,quantization is performed when the residual signal indicating adifference between the input signal and the predicted signal is coded.For this reason, when the QP is greater, an error is greater between theinput signal and the coded chroma signal or between the input image andthe decoded chroma signal. Especially as to the chroma signal, even aslight difference in value causes apparent color distortion in thesubjective image quality.

In order to solve the above problem, the image coding method in anaspect according to the present invention is a method of coding an inputblock included in an image. To be more specific, the image coding methodincludes: generating a predicted block by predicting the input block;calculating a residual block by subtracting the predicted block from theinput block; calculating quantized coefficients by performing transformand quantization on the residual block; calculating a coded residualblock by performing inverse quantization and inverse transform on thequantized coefficients; generating a temporary coded block by adding thecoded residual block to the predicted block; determining whether or notan offset process for correcting an error included in the temporarycoded block is required, to generate first flag information indicating aresult of the determination, the error being caused by the quantizationin the calculating of quantized coefficients; executing the offsetprocess on the temporary coded block when it is determined in thedetermining that the offset process is required; and performingvariable-length coding on the quantized coefficients and the first flaginformation.

With this configuration, an error (a quantization error) caused byquantization can be reduced. More specifically, the image quality can beeffectively prevented from deteriorating.

Moreover, the offset process may be executed to add an offset value to avalue of a pixel included in the temporary coded block. In thedetermining, whether an offset value for a previously-coded blockadjacent to the input block or the offset value newly calculated for thetemporary coded block is used in the offset process to be executed onthe temporary coded block may be further determined to generate secondflag information indicating a result of the determination. In theexecuting, the offset process may be executed on the temporary codedblock using the offset value indicated by the second flag information.In the performing, variable-length coding may be further performed onthe second flag information.

Furthermore, in the executing, the offset process may be executedselectively on a pixel (i) that is one of pixels included in thetemporary coded block and (ii) that corresponds to a pixel included inthe input block and having a value included in a predetermined rangewhere subjective color distortion is apparent.

Moreover, in the determining, when each of values of all pixels includedin the input block is outside the predetermined range, it may bedetermined that the offset process is not required to be executed on thetemporary coded block that corresponds to the input block.

As an example, each of the values of the pixels included in the inputblock may be expressed in a YUV format.

Furthermore, the image coding method may (i) switch between a codingprocess based on a first standard and a coding process based on a secondstandard, (ii) perform the determining, the executing, and theperforming, as the coding process based on the first standard, and (iii)code an identifier indicating a standard of a coding process.

The image decoding method in an aspect according to the presentinvention is a method of decoding a bitstream to generate a decodedblock. To be more specific, the image decoding method includes:obtaining quantized coefficients and first flag information thatindicates whether or not an offset process is required, by performingvariable-length decoding on the bitstream; obtaining a decoded residualblock by performing inverse quantization and inverse transform on thequantized coefficients; generating a predicted block by predicting thedecoded block; generating a temporary decoded block by adding thedecoded residual block to the predicted block; and generating thedecoded block by executing, on the temporary decoded block, the offsetprocess for correcting an error that is caused by quantization and isincluded in the temporary decoded block, when the first flag informationindicates that the offset process is required.

Moreover, the offset process may be executed to add an offset value to avalue of a pixel included in the temporary decoded block. In theobtaining of quantized coefficients and first flag information, secondflag information may be further obtained, the second flag informationindicating whether the offset value for a previously-decoded blockadjacent to the decoded block or the offset value newly calculated forthe temporary decoded block is used in the offset process to be executedon the temporary decoded block. In the generating of the decoded block,the offset process may be executed on the temporary decoded block usingthe offset value indicated by the second flag information.

As an example, each of values of pixels included in the decoded blockmay be expressed in a YUV format.

Furthermore, the image decoding method may (i) switch between a decodingprocess based on a first standard and a decoding process based on asecond standard, according to an identifier that is included in thebitstream and indicates the first standard or the second standard and(ii) perform, as the decoding process based on the first standard, theperforming and the executing when the identifier indicates the firststandard.

The image coding apparatus in an aspect according to the presentinvention codes an input block included in an image. To be morespecific, the image coding apparatus includes: a prediction unit whichgenerates a predicted block by predicting the input block; a calculationunit which calculates a residual block by subtracting the predictedblock from the input block; a transform-quantization unit whichcalculates quantized coefficients by performing transform andquantization on the residual block; an inverse quantization-transformunit which calculates a coded residual block by performing inversequantization and inverse transform on the quantized coefficients; ageneration unit which generates a temporary coded block by adding thecoded residual block to the predicted block; a determination unit whichdetermines whether or not an offset process for correcting an errorincluded in the temporary coded block is required, to generate firstflag information indicating a result of the determination, the errorbeing caused by the quantization performed by the transform-quantizationunit; an offset processing unit which executes the offset process on thetemporary coded block when it is determined by the determination unitthat the offset process is required; and a variable-length coding unitwhich performs variable-length coding on the quantized coefficients andthe first flag information.

The image decoding apparatus in an aspect according to the presentinvention decodes a bitstream to generate a decoded block. To be morespecific, the image decoding apparatus includes: a variable-lengthdecoding unit which obtains quantized coefficients and first flaginformation that indicates whether or not an offset process is required,by performing variable-length decoding on the bitstream; an obtainmentunit which obtains a decoded residual block by performing inversequantization and inverse transform on the quantized coefficients; aprediction unit which generates a predicted block by predicting thedecoded block; a generation unit which generates a temporary decodedblock by adding the decoded residual block to the predicted block; andan offset processing unit which generates the decoded block byexecuting, on the temporary decoded block, the offset process forcorrecting an error that is caused by quantization and is included inthe temporary decoded block, when the first flag information indicatesthat the offset process is required.

The image coding-decoding apparatus in an aspect according to thepresent invention includes: the image coding apparatus described above;and the image decoding apparatus described above.

It should be noted that a general or specific embodiment in an aspectmay be implemented by a system, a method, an integrated circuit, acomputer program, or a recording medium, or by any combination of asystem, a method, an integrated circuit, a computer program, and arecording medium.

The following is a description of embodiments according to the presentinvention, with reference to the drawings.

[Image Coding Apparatus]

FIG. 1 is a block diagram showing an example of a configuration of animage coding apparatus 200 in Embodiments 1 to 3 according to thepresent invention.

The image coding apparatus 200 performs compression coding on imagedata. For example, the image coding apparatus 200 receives, as an inputsignal, the image data for each block. The image coding apparatus 200generates a coded signal (i.e., a bitstream) by performing transform,quantization, and variable-length coding on the received input signal.

As shown in FIG. 1, the image coding apparatus 200 includes a subtracter205, a transform-quantization unit 210, an entropy coding unit 220, aninverse quantization-transform unit 230, an adder 235, a deblockingfilter 240, a memory 250, an intra prediction unit 260, a motionestimation unit 270, a motion compensation unit 280, and an intra/interselection switch 290.

The subtracter 205 calculates a difference between the input signal (aninput block) and the predicted signal (a predicted block). Morespecifically, the subtracter 205 calculates a prediction residual error(a residual block).

The transform-quantization unit 210 generates transform coefficients inthe frequency domain by transforming the prediction residual error inthe space domain. For example, the transform-quantization unit 210generates the transform coefficients by performing DCT (Discrete CosineTransform) on the prediction residual error. Moreover, thetransform-quantization unit 210 generates quantized coefficients byquantizing the transform coefficients.

The entropy coding unit 220 generates a coded signal by performingvariable-length coding on the quantized coefficients. Moreover, theentropy coding unit 220 codes motion data (such as a motion vector)estimated by the motion estimation unit 270, first flag information andsecond flag information (described later), an offset value (describedlater), and so forth. Then, the entropy coding unit 220 includes thesecoded data pieces into the coded signal and outputs this coded signal.

The inverse quantization-transform unit 230 restores the transformcoefficients by performing inverse quantization on the quantizedcoefficients. Moreover, the inverse quantization-transform unit 230restores the prediction residual error by performing inverse transformon the restored transform coefficients. It should be noted that sincethe information on the restored prediction residual error has been lostby quantization, the restored prediction residual error does not agreewith the prediction residual error generated by the subtracter 205. Tobe more specific, the restored prediction residual error includes aquantization error.

The adder 235 generates a local decoded image (a coded block) by addingthe restored prediction residual error to the predicted signal.

The deblocking filter 240 performs deblocking filtering on the generatedlocal decoded image.

The memory 250 stores a reference image to be used for motioncompensation. To be more specific, the memory 250 stores the localdecoded image on which deblocking filtering has been performed.

The intra prediction unit 260 generates a predicted signal (anintra-predicted signal) by performing intra prediction. Morespecifically, the intra prediction unit 260 generates theintra-predicted signal by performing intra prediction, with reference toan image located near a current block (the input signal) that is to becoded and is included in the local decoded image generated by the adder235.

The motion estimation unit 270 estimates motion data (such as a motionvector) between the input signal and the reference image stored in thememory 250.

The motion compensation unit 280 generates a predicted signal (aninter-predicted signal) by performing motion compensation based on theestimated motion data.

The intra/inter selection switch 290 selects one of the intra-predictedsignal and the inter-predicted signal, and outputs the selected signalas the predicted signal to the subtracter 205 and the adder 235.

With the configuration described thus far, the image coding apparatus200 in Embodiments 1 to 3 according to the present invention performscompression coding on the image data.

Embodiment 1

An image coding method in Embodiment 1 includes: generating a predictedblock by predicting the input block; calculating a residual block bysubtracting the predicted block from the input block; calculatingquantized coefficients by performing transform and quantization on theresidual block; calculating a coded residual block by performing inversequantization and inverse transform on the quantized coefficients;generating a temporary coded block by adding the coded residual block tothe predicted block; executing an offset process on the temporary codedblock; and performing variable-length coding on the quantizedcoefficients.

Note that the offset process refers to a process performed to correct anerror that is caused by quantization in the calculating of quantizedcoefficients and is included in the temporary coded block. To be morespecific, the offset process is executed to add an offset value to avalue of a pixel included in the temporary coded block. Here, althougheach of values of pixels included in the input block is not particularlylimited, the following description is based on the assumption that eachof the values of the pixels is expressed in the YUV format. Moreover,although the following describes an example where a predicted block isgenerated by intra prediction, the present invention is not limited tothis. The predicted block may be generated by, for example, interprediction.

The following describes a configuration of an image processing apparatus(a chroma-signal intra prediction unit) 500 that executes an intraprediction method in the offset process executed on the chroma signal inEmbodiment 1. FIG. 4 is a block diagram showing an example of theconfiguration of the image processing apparatus 500 in Embodiment 1according to the present invention. It should be noted that, asdescribed later, the image processing apparatus 500 in Embodiment 1according to the present invention corresponds to a part of the imagecoding apparatus 200 that performs compression coding on an image signaland outputs coded image data.

As shown in FIG. 4, the image processing apparatus 500 includes anintra-predicted chroma-signal generation unit 510, a residual signalcalculation unit 520, a transform-quantization unit 530, an inversequantization-transform unit 535, a temporary coded chroma-signalgeneration unit 540, a first DC component calculation unit 550, a secondDC component calculation unit 555, an offset value calculation unit 560,a coding unit 570, and an offset value addition unit 580.

An operation performed by the image processing apparatus 500 inEmbodiment 1 according to the present invention is described in moredetail, with reference to FIG. 5. FIG. 5 is a flowchart showing aprocess performed by the image processing apparatus 500.

Firstly, the intra-predicted chroma-signal generation unit 510 generatesan intra-predicted chroma signal based on an intra prediction mode, andoutputs the generated signal to the residual signal calculation unit 520and the temporary coded chroma-signal generation unit 540 (Step S5001).The intra-predicted chroma signal is generated according to the intraprediction mode using, as appropriate, a coded luma signal of aneighboring block, a coded chroma signal of a neighboring block, and acoded luma signal of the current block to be processed.

Next, the residual signal calculation unit 520 calculates a residualsignal from an input chroma signal and the intra-predicted chromasignal, and outputs the residual signal to the transform-quantizationunit 530 (Step S5002). The residual signal is obtained by calculating adifference between the input chroma signal and the intra-predictedchroma signal.

Next, the transform-quantization unit 530 calculates quantizedcoefficients by performing transform and quantization on the residualsignal, and outputs the quantized coefficients to the inversequantization-transform unit 535 and the coding unit 570 (Step S5003). Byquantization, the coefficient value in the frequency domain obtained bytransforming the residual signal is approximated more roughly. Here,when the QP is greater, rougher approximation is performed, meaning thatan error is greater between the original input chroma signal and thetemporary coded chroma signal described later.

Next, the inverse quantization-transform unit 535 calculates a codedresidual signal by performing inverse quantization and inverse transformon the quantized coefficients, and outputs the coded residual signal tothe temporary coded chroma-signal generation unit 540 (Step S5004).Inverse quantization and inverse transform are performed by a procedureexactly opposite to the procedure in Step S5003.

After this, the temporary coded chroma-signal generation unit 540generates a temporary coded chroma signal from the coded residual signaland the intra-predicted chroma signal, and outputs the generated signalto the second DC component calculation unit 555 and the offset valueaddition unit 580 (Step S5005). The temporary coded chroma signal iscalculated by adding the coded residual signal to the intra-predictedchroma signal.

Next, the first DC component calculation unit 550 calculates a DCcomponent of the input chroma signal and outputs the calculated DCcomponent to the offset value calculation unit 560 (Step S5006). Here,the DC component refers to an average value of a signal waveform, and isobtained by, for example, calculating an average value of pixels of theinput signal (i.e., a plurality of pixels included in the current blockto be coded). Alternatively, a DC component obtained by performingfrequency transform on the input chroma signal may be used as the DCcomponent of the input chroma signal.

Then, the second DC component calculation unit 555 calculates a DCcomponent of the temporary coded chroma signal, and outputs thecalculated DC component to the offset value calculation unit 560 (StepS5007). Here, the DC component is calculated by the same method as usedin Step S5006.

Next, the offset value calculation unit 560 calculates an offset valuefrom the DC component of the input chroma signal and the DC component ofthe temporary coded chroma signal, and outputs the calculated offsetvalue to the coding unit 570 and the offset value calculation unit 580(Step S5008). A specific method of calculating the offset value isdescribed later.

Then, the coding unit 570 generates a bitstream by coding the quantizedcoefficients, the intra prediction mode, and the offset value (StepS5009).

Next, the offset value addition unit 580 generates a coded chroma signalby adding the offset value to the temporary coded chroma signal (StepS5010). The coded chroma signal obtained by the addition performed bythe offset value addition unit 580 is stored into a memory, which is notillustrated, to be used in a later intra prediction process for example.

The process from Step S5001 to Step S5010 as described is repeated foreach of the blocks included in the image.

Here, the offset value is explained. The offset value of the DCcomponent of the input chroma signal and the DC component of thetemporary coded chroma signal is calculated according to Equation 1, forexample.

[Math. 1]

tmp_offset=average(InputC)−average(tmp Re cC)  Equation 1

Equation 1 shows an example where an average value of pixels of thechroma signal is used as the DC component. Here, “InputC” represents aninput chroma signal block, and “tmpRecC” represents a temporary codedchroma signal. Moreover, “average( )” represents a function used forcalculating the average of signal values of the input block. An offsetvalue “tmp_offset” is calculated with sub-pixel accuracy according toEquation 1 and, therefore, the coded chroma signal can be restored withhigh accuracy by using this offset value. However, the number of bits ofthe coded bitstream increases. Thus, in order to reduce the amount ofinformation, a quantization process or a clipping process is performedon the offset value as expressed by Equation 2.

[Math. 2]

offset=Clip(Disc(tmp_offset))  Equation 2

Here, “offset” represents an output value of the offset valuecalculation unit 560, that is, an offset value that is calculated withinteger-pixel accuracy and is actually added to the temporary codedchroma signal. Moreover, “Disc ( )” represents a function used forquantizing the offset value tmp_offset having sub-pixel accuracy into anintegral multiple of a parameter p1. Furthermore, “Clip ( )” representsa process of rounding a value outside a specified range to a maximumvalue or a minimum value using a parameter p2. FIG. 6 shows examples ofthe quantization process and the clipping process performed on theoffset value.

Here, each of the parameters p1 and p2 is an integer value. Each of theparameters p1 and p2 is determined according to, for example, limitationon the number of bits of the coded signal, manual setting based on thesubjective image quality of the coded image, a relationship with thequantized coefficients, and statistical data on a difference valuebetween the input chroma signal and the temporary coded chroma signal.

With this, the error between the input chroma signal and the codedchroma signal (that is, the error caused by quantization=thequantization error) can be reduced. Moreover, color distortion of thecoded chroma signal can be suppressed.

It should be noted that the coded chroma signal may be used inchroma-signal intra prediction, luma signal intra prediction,chroma-signal inter-frame prediction, or luma signal inter-frameprediction for a block to be processed later. With this, the predictionaccuracy can be further improved and the high coding efficiency can bethus implemented.

It should be noted that only one of the first DC component calculationunit 550 and the second DC component calculation unit 555 may be usedcommonly in calculating the DC component of the input chroma signal andthe DC component of the temporary coded chroma signal. This allows theimage processing apparatus 500 to be implemented with a smaller circuitsize.

It should be noted that the aforementioned offset process may also beperformed on the luma signal in the same way. As a result, a coded imagesignal closer in luma to the input signal can be obtained as well.

Embodiment 2

An image coding method in Embodiment 2 further includes: determiningwhether or not an offset process for correcting an error included in atemporary coded block is required, to generate first flag informationindicating a result of the determination, the error being caused by thequantization in the calculating of quantized coefficients. In theexecuting of the offset process, when it is determined in thedetermining that the offset process is required, the offset process isexecuted on the temporary coded block. Moreover, in the performing ofvariable-length coding, variable-length coding is performed on the firstflag information.

Next, an operation performed by an image processing apparatus (achroma-signal intra prediction unit) 600 in Embodiment 2 according tothe present invention is described.

FIG. 7 is a block diagram showing a configuration of the imageprocessing apparatus 600 in Embodiment 2.

As shown in FIG. 7, the image processing apparatus 600 includes anintra-predicted chroma-signal generation unit 610, a residual signalcalculation unit 620, a transform-quantization unit 630, an inversequantization-transform unit 635, a temporary coded chroma-signalgeneration unit 640, a first DC component calculation unit 650, a secondDC component calculation unit 655, an offset value calculation unit 660,a coding unit 670, an offset value addition unit 680, and an offsettingdetermination unit 690. More specifically, as compared with the imageprocessing apparatus 500 shown in FIG. 4, the image processing apparatus600 shown in FIG. 7 additionally includes the offsetting determinationunit 690. The other components of the image processing unit 600 areidentical to the corresponding components of the image processingapparatus 500 and, therefore, detailed explanations of these componentsare not repeated here.

The descriptions of the components that are included in the imageprocessing apparatus 600 and identical to the corresponding componentsincluded in the image processing apparatus 500 in Embodiment 1 areomitted. Thus, the offsetting determination unit 690 that is adifference between the image processing apparatus 600 and the imageprocessing apparatus 500 is described. To be more specific, inEmbodiment 2, whether or not the offset process is required isdetermined for each block and the offset value is calculated only forthe block where the offset process is determined to be required.

Next, chroma-signal intra prediction performed by the image processingapparatus 600 is described. FIG. 8 is a flowchart showing chroma-signalintra prediction according to the image coding method in Embodiment 2.Detailed explanations on processes shown in FIG. 8 that are identical tothe corresponding processes explained in Embodiment 1 with reference toFIG. 5 are not repeated here. Thus, Steps S6006 to S6010 in FIG. 8 aremainly described.

In Step S6006, the offsetting determination unit 690 determines whetheror not the offset process is required in the current block to beprocessed. For this determination, the input chroma signal and the inputluma signal are used for example. Color distortion caused by an errorbetween the input chroma signal and the coded chroma signal depends onthe values of the chroma signal and the luma signal. More specifically,even with the same error value, the color distortion appears differentlyin the subjective image quality according to the values of the chromasignal and luma signal. On account of this, the offset process isdetermined to be required when the input signal exists in a range (mayalso be referred to as “the range A” hereafter) where color distortionin the subjective image quality is apparent in the chroma space and theluma space.

A data structure of the range A may be expressed based on the maximumvalue and the minimum value for each component of YUV and RGB, or basedon a color map having three axes corresponding to YUV or RGB. Moreover,the input signal used for the determination may be, for example, averagevalues of the input chroma signal and the input luma signal in thecurrent block, DC components obtained by frequency transforms performedon the input chroma signal and the input luma signal, or median valuesof the input chroma signal and the input luma signal.

It should be noted that only the value in the chroma space may be usedin the determination as to whether or not the offset process is requiredin the current block. With this, the amount of calculation required ofthe offsetting determination unit 690 and the circuit size can besuppressed.

To be more specific, in the executing of the offset process, the offsetprocess may be executed selectively on a pixel: that is one of pixelsincluded in the temporary coded block; and that corresponds to a pixelincluded in the input block and having a value included in apredetermined range where subjective color distortion is apparent.Moreover, in the determining, when each of values of all pixels includedin the input block is outside the predetermined range, it may bedetermined that the offset process is not required to be executed on thetemporary coded block that corresponds to the input block.

When the offset process is determined to be required in Step S6006, theoffset value is calculated in Steps S6007 to S6009 in the same way as inEmbodiment 1.

On the other hand, when the offset process is determined not to berequired in Step S6006, the offset value is set at a value to which thecoding unit 670 assigns the minimum number of bits. With this,information indicating whether or not the offset process is requireddoes not need to be coded, and the determination as to whether or notthe offset process is required can be made with the minimum number ofbits. Thus, the number of bits of the bitstream can be suppressed, andcolor distortion of the coded chroma signal can also be suppressed. Notethat the information indicating whether or not the offset process isrequired (i.e., the first flag information) may be included in thebitstream separately from the offset value.

When the offset process is determined not to be required in Step S6006,the information indicating whether or not the offset process is required(i.e., the first flag information) may be coded. In this case, theprocess of adding the offset value in Step S6012 is not performed and,therefore, an increase in the amount of calculation can be suppressed.

It should be noted that, in Step S6006, whether or not the offsetprocess is required may be determined using the temporary coded chromasignal. The decoding apparatus side can also generate the same signal asthe temporary coded chroma signal and thus can determine whether or notthe offset process is required. On this account, the first flaginformation does not need to be included in the bitstream, and only theoffset value may be coded only when the offset process is required. Morespecifically, when the offset process is not required, the informationrelated to the offset process is not coded. This can further suppressthe number of bits of the bitstream.

It should be noted that the aforementioned offset process may also beperformed on the luma signal in the same way. As a result, a coded imagesignal closer in luma to the input signal can be obtained as well.

Embodiment 3

According to an image coding method in Embodiment 3, the followingprocess is further executed. More specifically, in the determining,whether an offset value for a previously-coded block adjacent to theinput block or the offset value newly calculated for the temporary codedblock is used in the offset process to be executed on the temporarycoded block is further determined (i.e., whether the offset value needsto be updated is determined) to generate second flag informationindicating a result of the determination. In the executing, the offsetprocess is executed on the temporary coded block using the offset valueindicated by the second flag information. In the performing,variable-length coding is further performed on the second flaginformation, and also on the new offset value when the offset value isupdated.

Next, an operation performed by an image processing apparatus (achroma-signal intra prediction unit) 700 in Embodiment 3 according tothe present invention is described.

FIG. 9 is a block diagram showing a configuration of the imageprocessing apparatus 700 in Embodiment 3.

As shown in FIG. 9, the image processing apparatus 700 includes anintra-predicted chroma-signal generation unit 710, a residual signalcalculation unit 720, a transform-quantization unit 730, an inversequantization-transform unit 735, a temporary coded chroma-signalgeneration unit 740, a first DC component calculation unit 750, a secondDC component calculation unit 755, an offset value calculation unit 760,a coding unit 770, an offset value addition unit 780, and aunit-of-offsetting determination unit 790. More specifically, ascompared with the image processing apparatus 500 shown in FIG. 4, theimage processing apparatus 700 shown in FIG. 9 additionally includes theunit-of-offsetting determination unit 790. The other components of theimage processing unit 700 are identical to the corresponding componentsof the image processing apparatus 500 and, therefore, detailedexplanations of these components are not repeated here.

The descriptions of the components that are included in the imageprocessing apparatus 700 and identical to the corresponding componentsincluded in the image processing apparatus 500 in Embodiment 1 areomitted. Thus, the unit-of-offsetting determination unit 790 that is adifference between the image processing apparatus 700 and the imageprocessing apparatus 500 is described. The image processing apparatus700 in Embodiment 3 allows the offset process to be performed on aplurality of neighboring blocks using the same offset value.

Next, chroma-signal intra prediction performed by the image processingapparatus 700 is described. FIG. 10 is a flowchart showing chroma-signalintra prediction according to the image coding method in Embodiment 3.Detailed explanations on processes that are identical to thecorresponding processes explained in Embodiment 1 with reference to FIG.5 are not repeated here. Thus, Steps S7009 to S7012 in FIG. 10 aremainly described.

In Step S7009, the unit-of-offsetting determination unit 790 determineswhether or not calculation of the offset value is completed for allblocks existing in an area including the blocks (also referred to as“the area A” hereafter). When calculation of the offset value is notcompleted for all the blocks (No in S7009), the image processingapparatus 700 stores the offset value calculated in Step S7008, andrepeats Steps S7001 to S7008. Then, when calculation of the offset valueis completed for all the blocks (Yes in S7009), the image processingapparatus 700 proceeds to Step S7010.

Next, in Step S7010, the unit-of-offsetting determination unit 790summarizes the offset values of all the blocks in the area A that arecalculated according to Steps up to S7009, to determine a unit of theoffset process. Then, the unit-of-offsetting determination unit 790outputs a result of the determination to the coding unit 770 and theoffset value addition unit 780.

After this, in Step S7011, the coding unit 770 generates a bitstream bycoding the quantized coefficients, the intra prediction mode, the unitof the offset process (second flag information), and the offset value.

Next, in Step S7012, the offset value addition unit 780 adds the offsetvalue to the temporary coded chroma signal to generate a coded chromasignal. The coded chroma signal generated by the offset addition unit780 is stored into a memory, which is not illustrated, to be used in alater intra prediction process for example.

Here, as an example, determination of a unit of the offset process isdescribed. Firstly, an evaluation formula represented by Equation 3 iscalculated for each of the offset values.

$\begin{matrix}{\left\lbrack {{Math}.\mspace{14mu} 3} \right\rbrack \mspace{551mu}} & \; \\{{{Eval}(k)} = {\sum\limits_{i = 1}^{N}{\left( {{jdg}\; 1(i) \times {{sBlk}(i)}} \right)/{\sum\limits_{i = 1}^{N}{{sBlk}(i)}}}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Here, “k” represents the offset value to be evaluated, “N” representsthe number of blocks existing in the area A, and “sBlk (i)” representsthe size of an i-th block in the area A. Moreover, “jdg1 (i)” representsa function used for determining whether or not the offset value of thei-th block in the area A is equal to “k”, as expressed by Equation 4.

$\begin{matrix}{\left\lbrack {{Math}.\mspace{14mu} 4} \right\rbrack \mspace{551mu}} & \; \\{{{jdg}\; 1(i)} = \left\{ \begin{matrix}{0,} & {{{if}\mspace{14mu} k} \neq {offset}} \\{1,} & {{{if}\mspace{14mu} k} = {offset}}\end{matrix} \right.} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Here, “Eval (k)” represents a proportion of pixels having the offsetvalue “k” in the area A.

Next, as expressed by Equation 5, whether or not the maximum value ofEval (k) is greater than or equal to a given threshold “Th_oft” isdetermined using a function “jdg2”.

$\begin{matrix}{\left\lbrack {{Math}.\mspace{14mu} 5} \right\rbrack \mspace{551mu}} & \; \\{{{jdg}\; 2} = \left\{ \begin{matrix}{0,} & {{{if}\mspace{14mu} {\max \left( {{Eval}(k)} \right)}} < {Th\_ oft}} \\{1,} & {{{if}\mspace{14mu} {\max \left( {{Eval}(k)} \right)}} \geq {Th\_ oft}}\end{matrix} \right.} & {{Equation}\mspace{14mu} 5}\end{matrix}$

Each of FIG. 11A and FIG. 11B shows an example of the result whenTh_oft=0.6. When jdg2=0, the unit-of-offsetting determination unit 790determines that a predominant offset value does not exist in the area Aand thus determines that the offset process is to be performed using adifferent offset value for each block as shown in FIG. 11A. On the otherhand, when jdg2=1, the unit-of-offsetting determination unit 790determines that a predominant offset value exists in the area A and thusdetermines that the offset process is to be performed on all the blocksusing the same offset value as shown in FIG. 11B.

As a result, the offset values of an area larger than a block (such asan LCU) can be coded by one operation. This can suppress an increase inthe number of bits of the coded signal and also suppress colordistortion of the coded chroma signal.

It should be noted that the determination of the unit of the offsetprocess may be made based on a comparison using a cost function asexpressed by Equation 6.

$\begin{matrix}{\left\lbrack {{Math}.\mspace{14mu} 6} \right\rbrack \mspace{551mu}} & \; \\{{Cost} = {{\sum\limits_{i = 0}^{N}{{diff}\left( {{{Input}(i)},{{oftRec}(i)}} \right)}} + {\lambda \times {\sum\limits_{i = 0}^{N}{{bits}\left( {{oftRec}(i)} \right)}}}}} & {{Equation}\mspace{14mu} 6}\end{matrix}$

Here, “Input (i)” represents an i-th block in the area A of the inputsignal, and “oftRec (i)” represents an i-th block in the area A of thecoded signal. Here, only the chroma signal or both the luma signal andthe chroma signal may be used. Moreover, “diff (A, B)” represents afunction that returns a difference value between a block A and a blockB. The difference value is obtained by calculating an absolute error,for example. Furthermore, “bit (A)” is a function that returns thenumber of bits generated when the block A is coded. Moreover, “λ”represents a weighting parameter and is set according to, for example,the QP.

For example, the unit-of-offsetting determination unit 790 performscalculation according to Equation 6 for each of the cases: where thesame offset value is used for all the blocks; and where a differentoffset value is used for each of the blocks. Then, by making acomparison as expressed by Equation 7, the unit-of-offsettingdetermination unit 790 determines the unit of the offset process.

$\begin{matrix}{\left\lbrack {{Math}.\mspace{14mu} 7} \right\rbrack \mspace{551mu}} & \; \\{{{jdg}\; 3} = \left\{ \begin{matrix}{0,} & {{{if}\mspace{14mu} {cost\_ inv}} < {cost\_ all}} \\{1,} & {{{if}\mspace{14mu} {cost\_ inv}} \geq {cost\_ all}}\end{matrix} \right.} & {{Equation}\mspace{14mu} 7}\end{matrix}$

Here, “cost_inv” represents a cost value of Equation 6 in the case wherea different offset value is used for each of the blocks, and “cost_all”represents a cost value of Equation 6 in the case where the same offsetvalue is used for all the blocks of the area A. When jdg3=0, theunit-of-offsetting determination unit 790 determines that the offsetprocess is to be performed using a different offset value for each ofthe blocks. On the other hand, when jdg3=1, the unit-of-offsettingdetermination unit 790 determines that the offset process is to beperformed using the same offset value for all the blocks. As a result,coding can be performed, with the number of bits and the appearance ofcolor distortion being in balance.

It should be noted that, as described in Embodiment 2, coding of theoffset value may be performed only on a block where the offset processis required. To be more specific, when the offset process is notrequired, the offset value of this block is not coded. With this, thenumber of bits of the coded signal can be further suppressed.

It should be noted that the aforementioned offset process may also beperformed on the luma signal in the same way. As a result, a coded imagesignal closer in luma to the input signal can be obtained as well.

[Image Decoding Apparatus]

FIG. 12 is a block diagram showing an example of a configuration of animage decoding apparatus 400 in Embodiments 4 to 6 according to thepresent invention.

The image decoding apparatus 400 decodes coded image data generated bycompression coding. For example, the image decoding apparatus 400receives the coded image data for each block, as a current signal to bedecoded. The image decoding apparatus 400 restores the image data byperforming variable-length decoding, inverse quantization, and inversetransform on the received current signal to be decoded.

As shown in FIG. 4, the image decoding apparatus 400 includes an entropydecoding unit 410, an inverse quantization-transform unit 420, an adder425, a deblocking filter 430, a memory 440, an intra prediction unit450, a motion compensation unit 460, and an intra/inter selection switch470.

The entropy decoding unit 410 restores the quantized coefficients byperforming variable-length decoding on an input signal (an inputstream). Here, the input signal (the input stream) is a current signalto be decoded and corresponds to data of each block included in thecoded image data. Moreover, the entropy decoding unit 410 obtains motiondata from the input signal and outputs the obtained motion data to themotion compensation unit 460.

The inverse quantization-transform unit 420 restores the transformcoefficients by performing inverse quantization on the quantizedcoefficients restored by the entropy decoding unit 410. Then, theinverse quantization-transform unit 420 restores the prediction residualerror by performing inverse transform on the restored transformcoefficients.

The adder 425 generates a decoded image by adding the predictionresidual error restored by the inverse quantization-transform unit 420to a predicted signal obtained from the intra/inter selection switch470.

The deblocking filter 430 performs deblocking filtering on the decodedimage generated by the adder 425. The decoded image on which deblockingfiltering has been performed is outputted as a decoded signal.

The memory 440 stores a reference image to be used for motioncompensation. To be more specific, the memory 440 stores the decodedimage on which deblocking filtering has been performed by the deblockingfilter 430.

The intra prediction unit 450 generates a predicted signal (anintra-predicted signal) by performing intra prediction. Morespecifically, the intra prediction unit 450 generates theintra-predicted signal, by performing intra prediction with reference toan image located near a current block that is to be decoded (the inputsignal) and is included in the decoded image generated by the adder 425.

The motion compensation unit 460 generates a predicted signal (aninter-predicted signal) by performing motion compensation based on themotion data outputted from the entropy decoding unit 410.

The intra/inter selection switch 470 selects one of the intra-predictedsignal and the inter-predicted signal, and outputs the selected signalas the predicted signal to the adder 425.

With the configuration described thus far, the image decoding apparatus400 in Embodiments 4 to 6 according to the present invention decodes thecoded image data generated by compression coding.

Embodiment 4

An image decoding method in Embodiment 4 includes: obtaining quantizedcoefficients by performing variable-length decoding on the bitstream;obtaining a decoded residual block by performing inverse quantizationand inverse transform on the quantized coefficients; generating apredicted block by predicting the decoded block; generating a temporarydecoded block by adding the decoded residual block to the predictedblock; and generating the decoded block by executing, on the temporarydecoded block, the offset process for correcting an error that is causedby quantization and is included in the temporary decoded block.

The following describes a configuration of an image processing apparatus(a chroma-signal intra prediction unit) 800 that executes an intraprediction method in the offset process executed on the chroma signal inEmbodiment 4. FIG. 15 is a block diagram showing an example of theconfiguration of the image processing apparatus 800 in Embodiment 4according to the present invention. It should be noted that, asdescribed later, the image processing apparatus 800 in Embodiment 4according to the present invention corresponds to a part of the imagedecoding apparatus that decodes a coded signal and outputs decoded imagedata.

As shown in FIG. 15, the image processing apparatus 800 includes avariable-length decoding unit 810, a residual signal obtainment unit820, an intra-predicted chroma-signal generation unit 830, a temporarydecoded chroma-signal generation unit 840, and an offset value additionunit 850.

An operation performed by the image processing apparatus 800 inEmbodiment 4 according to the present invention is described in moredetail, with reference to FIG. 16. FIG. 16 is a flowchart showing aprocess performed by the image processing apparatus 800.

Firstly, the variable-length decoding unit 810 obtains quantizedcoefficients, an intra prediction mode, and an offset value byperforming variable-length decoding on the bitstream, and outputs theobtained quantized coefficients, intra prediction mode, and offset valueto the residual signal obtainment unit 820 and the offset value additionunit 850 (Step S8001).

Next, the residual signal obtainment unit 820 obtains a decoded residualsignal by performing inverse quantization and inverse transform on thequantized coefficients, and outputs the decoded residual signal to thetemporary decoded chroma-signal generation unit 840 (Step S8002). Thedecoded residual signal has been approximated more roughly by thequantization at the time of coding. On account of this, when the decodedchroma signal is generated using this residual signal, an error withrespect to the yet-to-be-coded input image is caused.

Next, the intra-predicted chroma-signal generation unit 830 generates anintra-predicted chroma signal based on the intra prediction mode of thechroma signal, and outputs the intra-predicted chroma signal to thetemporary decoded chroma-signal generation unit 840 (Step S8003). Theintra prediction mode of the chroma signal is indicated as an indexnumber assigned to a generation method of the intra-predicted chromasignal. The intra prediction mode is determined for each block in intraprediction performed at the time of coding. The intra-predicted chromasignal is generated using, as appropriate, a coded luma signal of aneighboring block, a coded chroma signal of a neighboring block, and acoded luma signal of the current block to be processed.

Next, the temporary decoded chroma-signal generation unit 840 generatesa temporary decoded chroma signal from the decoded residual signal andthe intra-predicted chroma signal (Step S8004). The temporary decodedchroma signal is calculated by adding the decoded residual signal to theintra-predicted chroma signal.

Next, the offset value addition unit 850 generates a decoded chromasignal by adding the offset value to the temporary decoded chroma signal(Step S8006). Note that the offset value is calculated when intraprediction is made at the time of coding. The decoded chroma signalgenerated by the offset value addition unit 850 is stored into a memory,which is not illustrated, to be used in a later intra prediction processfor example.

With this, an error between the yet-to-be-coded input chroma signal andthe decoded chroma signal can be reduced. Moreover, color distortion ofthe decoded chroma signal can be suppressed.

It should be noted that the aforementioned offset process may also beperformed on the luma signal in the same way. As a result, a coded imagesignal closer in luma to the input signal can be obtained as well.

FIG. 21 is a diagram showing an example where Embodiment 4 according tothe present invention is shown as a syntax based on the HEVC standard(see Non Patent Literature 3). When an image signal in the YUV format iscoded, offset values of U and V components are decoded for each unit ofprediction after the intra prediction mode of the chroma signal isdecoded.

Embodiment 5

An image decoding method in Embodiment 5 further executes the followingprocess. More specifically, in the performing of variable-lengthdecoding, first flag information indicating whether or not the offsetprocess is required is further obtained. In the executing of the offsetprocess, the offset process is executed when the first flag informationindicates that the offset process is required.

Next, an operation performed by an image processing apparatus (achroma-signal intra prediction unit) 900 in Embodiment 5 according tothe present invention is described.

FIG. 17 is a block diagram showing a configuration of the imageprocessing apparatus 900 in Embodiment 5.

As shown in FIG. 17, the image processing apparatus 900 includes avariable-length decoding unit 910, a residual signal obtainment unit920, a temporary decoded chroma-signal generation unit 930, anintra-predicted chroma-signal generation unit 940, an offset valueaddition unit 950, and an offsetting determination unit 960. Morespecifically, as compared with the image processing apparatus 800 shownin FIG. 15, the image processing apparatus 900 shown in FIG. 17additionally includes the offsetting determination unit 960. The othercomponents of the image processing unit 900 are identical to thecorresponding components of the image processing apparatus 800 and,therefore, detailed explanations of these components are not repeatedhere.

The descriptions of the components that are included in the imageprocessing apparatus 900 and identical to the corresponding componentsincluded in the image processing apparatus 800 in Embodiment 4 areomitted. Thus, the offsetting determination unit 970 that is adifference between the image processing apparatus 900 and the imageprocessing apparatus 800 is described. To be more specific, inEmbodiment 5, whether or not the offset process is required isdetermined and the offset process is executed only on the block wherethe offset process is required.

Next, chroma-signal intra prediction performed by the image processingapparatus 900 is described. FIG. 18 is a flowchart showing chroma-signalintra prediction according to the image coding method in Embodiment 5.Detailed explanations on processes shown in FIG. 18 that are identicalto the corresponding processes explained in Embodiment 4 with referenceto FIG. 16 are not repeated here. Thus, Steps S9005 to S9007 in FIG. 18are mainly described.

In Step S9005, the offsetting determination unit 960 determines, usingthe decoded luma signal and the temporary decoded chroma signal of thecurrent block, whether or not the offset process is required. Thisdetermination is made according to, for example, the same method as usedin Embodiment 2. Color distortion caused to the decoded chroma signal byan error between the yet-to-be-coded input chroma signal and the decodedchroma signal depends on the values of the chroma signal and the lumasignal. More specifically, even with the same error value, the colordistortion appears differently in the subjective image quality accordingto the values of the chroma signal and luma signal. On account of this,the offsetting determination unit 960 determines that the offset processis required when the temporary decoded signal exists in a range (mayalso be referred to as “the range A” hereafter) where color distortionin the subjective image quality is apparent in the chroma space and theluma space.

A data structure of the range A may be expressed based on the maximumvalue and the minimum value for each component of YUV and RGB, or basedon a color map having three axes corresponding to YUV or RGB. Moreover,the input signal used for the determination may be, for example, averagevalues of the input chroma signal and the input luma signal in thecurrent block, DC components obtained by frequency transforms performedon the input chroma signal and the input luma signal, or median valuesof the input chroma signal and the input luma signal.

Then, when it is determined in Step S9005 that the offset process isrequired, Steps S9006 to S9007 are performed. In Step S9006, thevariable-length decoding unit 910 obtains the offset value by performingvariable-length decoding on the bitstream, and outputs the obtainedoffset value to the offset value addition unit 950.

Next, in Step S9007, the offset value addition unit 950 generates adecoded chroma signal by adding the offset value to the temporarydecoded chroma signal. The decoded chroma signal generated by the offsetvalue addition unit 950 is stored into a memory, which is notillustrated in the diagram, to be used for a later intra predictionprocess, for example.

On the other hand, when it is determined in Step S9005 that the offsetprocess is not required, the offset process is not performed. Thus, thetemporary decoded chroma signal is used as the decoded chroma signalwithout change.

With this, color distortion of the coded chroma signal can be suppressedwhile the number of bits of the bitstream is suppressed.

It should be noted that the aforementioned offset process may also beperformed on the luma signal in the same way. As a result, a coded imagesignal closer in luma to the input signal can be obtained as well.

A method of determining whether or not the offset process is required isnot limited to the aforementioned method. For example, the offsettingdetermination unit 960 obtains, from the bitstream, first flaginformation indicating whether or not the offset process is required.Then, whether or not the offset process is required may be determinedaccording to the value set in the obtained first flag information.

Embodiment 6

An image decoding method in Embodiment 6 further performs the followingprocess. To be more specific, in the obtaining of quantized coefficientsand first flag information, second flag information is further obtained,the second flag information indicating whether the offset value for apreviously-decoded block adjacent to the decoded block or the offsetvalue newly calculated for the temporary decoded block is used in theoffset process to be executed on the temporary decoded block (i.e., thesecond flag information indicating whether or not the offset value needsto be updated). In the generating of the decoded block, the offsetprocess is executed on the temporary decoded block using the offsetvalue indicated by the second flag information.

Next, an operation performed by an image processing apparatus (achroma-signal intra prediction unit) 1000 in Embodiment 6 according tothe present invention is described.

FIG. 19 is a block diagram showing a configuration of the imageprocessing apparatus 1000 in Embodiment 6.

As shown in FIG. 19, the image processing apparatus 1000 includes avariable-length decoding unit 1010, a residual signal obtainment unit1020, an intra-predicted chroma-signal generation unit 1030, a temporarydecoded chroma-signal generation unit 1040, an offset value additionunit 1060, and a unit-of-offsetting information obtainment unit 1070.More specifically, as compared with the image processing apparatus 800shown in FIG. 15, the image processing apparatus 1000 additionallyincludes the unit-of-offsetting information obtainment unit 1070. Theother components of the image processing unit 1000 are identical to thecorresponding components of the image processing apparatus 800 and,therefore, detailed explanations of these components are not repeatedhere.

The descriptions of the components that are included in the imageprocessing apparatus 1000 and identical to the corresponding componentsincluded in the image processing apparatus 800 in Embodiment 4 areomitted. Thus, the unit-of-offsetting information obtainment unit 1070that is a difference between the image processing apparatus 1000 and theimage processing apparatus 800 is described. The image processingapparatus 1000 in Embodiment 6 allows the offset process to be performedon a plurality of neighboring blocks using the same offset value.

Next, chroma-signal intra prediction performed by the image processingapparatus 1000 is described. FIG. 20 is a flowchart showingchroma-signal intra prediction according to the image decoding method inEmbodiment 6. Detailed explanations on processes that are identical tothe corresponding processes explained in Embodiment 4 with reference toFIG. 16 are not repeated here. Thus, Step S10001 and Steps S10005 toS10007 in FIG. 20 are mainly described.

In Step S10001, the variable-length decoding unit 1010 obtains quantizedcoefficients, an intra prediction mode, and unit-of-offsettinginformation by performing variable-length decoding on the bitstream, andoutputs the obtained quantized coefficients, intra prediction mode, andunit-of-offsetting information to the residual signal obtainment unit1020, the intra-predicted chroma-signal generation unit 1030, theunit-of-offsetting information obtainment unit 1070, and the offsetvalue addition unit 1060. The unit-of-offsetting information refers toinformation about whether, in an area A including a plurality of blocks,the same offset value is used for all the blocks or a different offsetvalue is used for each of the blocks.

Next, in Step S10005, the unit-of-offsetting information obtainment unit1070 verifies, from the unit-of-offsetting information, whether or notthe offset value needs to be updated and outputs the result to thevariable-length decoding unit 1010. When the same offset value is usedfor all the blocks of the area A, the offset value is updated only whenthe offset process is completed for all the blocks of the area A. On theother hand, when a different offset value is used for each of the blocksof the area A, the offset value is updated for each of the blocks.

When the offset value needs to be updated, the variable-length decodingunit 1010 obtains the offset value by performing variable-lengthdecoding on the bitstream and outputs the obtained offset value to theoffset value addition unit 1060 in Step S10006. Here, the offset valueis calculated when intra prediction is made at the time of coding.

Next, in Step S10007, the offset value addition unit 1060 generates adecoded chroma signal by adding the offset value to the temporarydecoded chroma signal.

As a result, the offset values of an area larger than a block can becoded by one operation. This can suppress an increase in the number ofbits of the coded signal and also suppress color distortion of thedecoded chroma signal.

It should be noted that the aforementioned offset process may also beperformed on the luma signal in the same way. As a result, a coded imagesignal closer in luma to the input signal can be obtained as well.

FIG. 22 is a diagram showing an example where Embodiment 6 according tothe present invention is shown as a syntax based on the HEVC standard(see Non Patent Literature 3). When an image signal in the YUV format iscoded, offset values of U and V components are decoded for each codingtree (a group of units of coding) in the case of an I-slice, after theintra prediction mode of the chroma signal is decoded.

Embodiment 7

The processing described in each of embodiments can be simplyimplemented in an independent computer system, by recording, in arecording medium, a program for implementing the configurations of themoving picture coding method (image coding method) and the movingpicture decoding method (image decoding method) described in each ofembodiments. The recording media may be any recording media as long asthe program can be recorded, such as a magnetic disk, an optical disk, amagnetic optical disk, an IC card, and a semiconductor memory.

Hereinafter, the applications to the moving picture coding method (imagecoding method) and the moving picture decoding method (image decodingmethod) described in each of embodiments and systems using thereof willbe described. The system has a feature of having an image coding anddecoding apparatus that includes an image coding apparatus using theimage coding method and an image decoding apparatus using the imagedecoding method. Other configurations in the system can be changed asappropriate depending on the cases.

FIG. 23 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106, ex107, ex108, ex109, and ex110 which arefixed wireless stations are placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via the Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110, respectively.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 23, and a combination inwhich any of the elements are connected is acceptable. In addition, eachdevice may be directly connected to the telephone network ex104, ratherthan via the base stations ex106 to ex110 which are the fixed wirelessstations. Furthermore, the devices may be interconnected to each othervia a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing video. A camera ex116, such as a digital camera, is capable ofcapturing both still images and video. Furthermore, the cellular phoneex114 may be the one that meets any of the standards such as GlobalSystem for Mobile Communications (GSM) (registered trademark), CodeDivision Multiple Access (CDMA), Wideband-Code Division Multiple Access(W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of images of alive show and others. In such a distribution, a content (for example,video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camerafunctions as the image coding apparatus according to an aspect of thepresent invention), and the coded content is transmitted to thestreaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to theclients upon their requests. The clients include the computer ex111, thePDA ex112, the camera ex113, the cellular phone ex114, and the gamemachine ex115 that are capable of decoding the above-mentioned codeddata. Each of the devices that have received the distributed datadecodes and reproduces the coded data (i.e., functions as the imagedecoding apparatus according to an aspect of the present invention).

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and video captured by not only the camera ex113 but alsothe camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, the coding and decoding processes may be performed by anLSI ex500 generally included in each of the computer ex111 and thedevices. The LSI ex500 may be configured of a single chip or a pluralityof chips. Software for coding and decoding video may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, anda hard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients may receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

Aside from the example of the content providing system ex100, at leastone of the moving picture coding apparatus (image coding apparatus) andthe moving picture decoding apparatus (image decoding apparatus)described in each of embodiments may be implemented in a digitalbroadcasting system ex200 illustrated in FIG. 24. More specifically, abroadcast station ex201 communicates or transmits, via radio waves to abroadcast satellite ex202, multiplexed data obtained by multiplexingaudio data and others onto video data. The video data is data coded bythe moving picture coding method described in each of embodiments (i.e.,data coded by the image coding apparatus according to an aspect of thepresent invention). Upon receipt of the multiplexed data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 with a satellite broadcast reception function receives theradio waves. Next, a device such as a television (receiver) ex300 and aset top box (STB) ex217 decodes the received multiplexed data, andreproduces the decoded data (i.e., functions as the image decodingapparatus according to an aspect of the present invention).

Furthermore, a reader/recorder ex218 (i) reads and decodes themultiplexed data recorded on a recording medium ex215, such as a DVD anda BD, or (i) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data. The reader/recorder ex218 can include the moving picturedecoding apparatus or the moving picture coding apparatus as shown ineach of embodiments. In this case, the reproduced video signals aredisplayed on the monitor ex219, and can be reproduced by another deviceor system using the recording medium ex215 on which the multiplexed datais recorded. It is also possible to implement the moving picturedecoding apparatus in the set top box ex217 connected to the cable ex203for a cable television or to the antenna ex204 for satellite and/orterrestrial broadcasting, so as to display the video signals on themonitor ex219 of the television ex300. The moving picture decodingapparatus may be implemented not in the set top box but in thetelevision ex300.

FIG. 25 illustrates the television (receiver) ex300 that uses the movingpicture coding method and the moving picture decoding method describedin each of embodiments. The television ex300 includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audiodata onto video data, through the antenna ex204 or the cable ex203, etc.that receives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes videodata and audio data coded by a signal processing unit ex306 into data.

The television ex300 further includes: a signal processing unit ex306including an audio signal processing unit ex304 and a video signalprocessing unit ex305 that decode audio data and video data and codeaudio data and video data, respectively (which function as the imagecoding apparatus and the image decoding apparatus according to theaspects of the present invention); and an output unit ex309 including aspeaker ex307 that provides the decoded audio signal, and a display unitex308 that displays the decoded video signal, such as a display.Furthermore, the television ex300 includes an interface unit ex317including an operation input unit ex312 that receives an input of a useroperation. Furthermore, the television ex300 includes a control unitex310 that controls overall each constituent element of the televisionex300, and a power supply circuit unit ex311 that supplies power to eachof the elements. Other than the operation input unit ex312, theinterface unit ex317 may include: a bridge ex313 that is connected to anexternal device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SDcard; a driver ex315 to be connected to an external recording medium,such as a hard disk; and a modem ex316 to be connected to a telephonenetwork. Here, the recording medium ex216 can electrically recordinformation using a non-volatile/volatile semiconductor memory elementfor storage. The constituent elements of the television ex300 areconnected to each other through a synchronous bus.

First, the configuration in which the television ex300 decodesmultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon a user operation through a remote controllerex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside, respectively. When the output unit ex309 provides thevideo signal and the audio signal, the signals may be temporarily storedin buffers ex318 and ex319, and others so that the signals arereproduced in synchronization with each other. Furthermore, thetelevision ex300 may read multiplexed data not through a broadcast andothers but from the recording media ex215 and ex216, such as a magneticdisk, an optical disk, and a SD card. Next, a configuration in which thetelevision ex300 codes an audio signal and a video signal, and transmitsthe data outside or writes the data on a recording medium will bedescribed. In the television ex300, upon a user operation through theremote controller ex220 and others, the audio signal processing unitex304 codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310 using thecoding method described in each of embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in thebuffers ex320 and ex321, and others so that the signals are reproducedin synchronization with each other. Here, the buffers ex318, ex319,ex320, and ex321 may be plural as illustrated, or at least one buffermay be shared in the television ex300. Furthermore, data may be storedin a buffer so that the system overflow and underflow may be avoidedbetween the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be capable of only receiving, decoding, andproviding outside data but not the coding, multiplexing, and providingoutside data.

Furthermore, when the reader/recorder ex218 reads or writes multiplexeddata from or on a recording medium, one of the television ex300 and thereader/recorder ex218 may decode or code the multiplexed data, and thetelevision ex300 and the reader/recorder ex218 may share the decoding orcoding.

As an example, FIG. 26 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or onan optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406,and ex407 to be described hereinafter. The optical head ex401 irradiatesa laser spot in a recording surface of the recording medium ex215 thatis an optical disk to write information, and detects reflected lightfrom the recording surface of the recording medium ex215 to read theinformation. The modulation recording unit ex402 electrically drives asemiconductor laser included in the optical head ex401, and modulatesthe laser light according to recorded data. The reproductiondemodulating unit ex403 amplifies a reproduction signal obtained byelectrically detecting the reflected light from the recording surfaceusing a photo detector included in the optical head ex401, anddemodulates the reproduction signal by separating a signal componentrecorded on the recording medium ex215 to reproduce the necessaryinformation. The buffer ex404 temporarily holds the information to berecorded on the recording medium ex215 and the information reproducedfrom the recording medium ex215.

The disk motor ex405 rotates the recording medium ex215. The servocontrol unit ex406 moves the optical head ex401 to a predeterminedinformation track while controlling the rotation drive of the disk motorex405 so as to follow the laser spot. The system control unit ex407controls overall the information reproducing/recording unit ex400. Thereading and writing processes can be implemented by the system controlunit ex407 using various information stored in the buffer ex404 andgenerating and adding new information as necessary, and by themodulation recording unit ex402, the reproduction demodulating unitex403, and the servo control unit ex406 that record and reproduceinformation through the optical head ex401 while being operated in acoordinated manner. The system control unit ex407 includes, for example,a microprocessor, and executes processing by causing a computer toexecute a program for read and write.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 27 illustrates the recording medium ex215 that is the optical disk.On the recording surface of the recording medium ex215, guide groovesare spirally formed, and an information track ex230 records, in advance,address information indicating an absolute position on the diskaccording to change in a shape of the guide grooves. The addressinformation includes information for determining positions of recordingblocks ex231 that are a unit for recording data. Reproducing theinformation track ex230 and reading the address information in anapparatus that records and reproduces data can lead to determination ofthe positions of the recording blocks. Furthermore, the recording mediumex215 includes a data recording area ex233, an inner circumference areaex232, and an outer circumference area ex234. The data recording areaex233 is an area for use in recording the user data. The innercircumference area ex232 and the outer circumference area ex234 that areinside and outside of the data recording area ex233, respectively arefor specific use except for recording the user data. The informationreproducing/recording unit 400 reads and writes coded audio, coded videodata, or multiplexed data obtained by multiplexing the coded audio andvideo data, from and on the data recording area ex233 of the recordingmedium ex215.

Although an optical disk having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disk is notlimited to such, and may be an optical disk having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disk may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disk and for recording information havingdifferent layers from various angles.

Furthermore, a car ex210 having an antenna ex205 can receive data fromthe satellite ex202 and others, and reproduce video on a display devicesuch as a car navigation system ex211 set in the car ex210, in thedigital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be a configuration, for example, includinga GPS receiving unit from the configuration illustrated in FIG. 25. Thesame will be true for the configuration of the computer ex111, thecellular phone ex114, and others.

FIG. 28A illustrates the cellular phone ex114 that uses the movingpicture coding method and the moving picture decoding method describedin embodiments. The cellular phone ex114 includes: an antenna ex350 fortransmitting and receiving radio waves through the base station ex110; acamera unit ex365 capable of capturing moving and still images; and adisplay unit ex358 such as a liquid crystal display for displaying thedata such as decoded video captured by the camera unit ex365 or receivedby the antenna ex350. The cellular phone ex114 further includes: a mainbody unit including an operation key unit ex366; an audio output unitex357 such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still pictures, e-mails, or others; and aslot unit ex364 that is an interface unit for a recording medium thatstores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 28B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keyunit ex366 is connected mutually, via a synchronous bus ex370, to apower supply circuit unit ex361, an operation input control unit ex362,a video signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Then, themodulation/demodulation unit ex352 performs spread spectrum processingon the digital audio signals, and the transmitting and receiving unitex351 performs digital-to-analog conversion and frequency conversion onthe data, so as to transmit the resulting data via the antenna ex350.Also, in the cellular phone ex114, the transmitting and receiving unitex351 amplifies the data received by the antenna ex350 in voiceconversation mode and performs frequency conversion and theanalog-to-digital conversion on the data. Then, themodulation/demodulation unit ex352 performs inverse spread spectrumprocessing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via theaudio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation key unitex366 and others of the main body is sent out to the main control unitex360 via the operation input control unit ex362. The main control unitex360 causes the modulation/demodulation unit ex352 to perform spreadspectrum processing on the text data, and the transmitting and receivingunit ex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving picture coding method shown in each of embodiments (i.e.,functions as the image coding apparatus according to the aspect of thepresent invention), and transmits the coded video data to themultiplexing/demultiplexing unit ex353. In contrast, during when thecamera unit ex365 captures video, still images, and others, the audiosignal processing unit ex354 codes audio signals collected by the audioinput unit ex356, and transmits the coded audio data to themultiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit(modulation/demodulation circuit unit) ex352 performs spread spectrumprocessing on the multiplexed data, and the transmitting and receivingunit ex351 performs digital-to-analog conversion and frequencyconversion on the data so as to transmit the resulting data via theantenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using amoving picture decoding method corresponding to the moving picturecoding method shown in each of embodiments (i.e., functions as the imagedecoding apparatus according to the aspect of the present invention),and then the display unit ex358 displays, for instance, the video andstill images included in the video file linked to the Web page via theLCD control unit ex359. Furthermore, the audio signal processing unitex354 decodes the audio signal, and the audio output unit ex357 providesthe audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably have 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding apparatus. Althoughthe digital broadcasting system ex200 receives and transmits themultiplexed data obtained by multiplexing audio data onto video data inthe description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picturedecoding method in each of embodiments can be used in any of the devicesand systems described. Thus, the advantages described in each ofembodiments can be obtained.

Furthermore, the present invention is not limited to embodiments, andvarious modifications and revisions are possible without departing fromthe scope of the present invention.

Embodiment 8

Video data can be generated by switching, as necessary, between (i) themoving picture coding method or the moving picture coding apparatusshown in each of embodiments and (ii) a moving picture coding method ora moving picture coding apparatus in conformity with a differentstandard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconform cannot be detected, there is a problem that an appropriatedecoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexingaudio data and others onto video data has a structure includingidentification information indicating to which standard the video dataconforms. The specific structure of the multiplexed data including thevideo data generated in the moving picture coding method and by themoving picture coding apparatus shown in each of embodiments will behereinafter described. The multiplexed data is a digital stream in theMPEG-2 Transport Stream format.

FIG. 29 illustrates a structure of the multiplexed data. As illustratedin FIG. 29, the multiplexed data can be obtained by multiplexing atleast one of a video stream, an audio stream, a presentation graphicsstream (PG), and an interactive graphics stream. The video streamrepresents primary video and secondary video of a movie, the audiostream (IG) represents a primary audio part and a secondary audio partto be mixed with the primary audio part, and the presentation graphicsstream represents subtitles of the movie. Here, the primary video isnormal video to be displayed on a screen, and the secondary video isvideo to be displayed on a smaller window in the primary video.Furthermore, the interactive graphics stream represents an interactivescreen to be generated by arranging the GUI components on a screen. Thevideo stream is coded in the moving picture coding method or by themoving picture coding apparatus shown in each of embodiments, or in amoving picture coding method or by a moving picture coding apparatus inconformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1. The audio stream is coded in accordance with a standard, such asDolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1B00 to0x1B1F are allocated to the video streams to be used for secondary videoof the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams tobe used for the secondary audio to be mixed with the primary audio.

FIG. 30 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 31 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 31 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 31, the video stream is divided into pictures as I pictures, Bpictures, and P pictures each of which is a video presentation unit, andthe pictures are stored in a payload of each of the PES packets. Each ofthe PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 32 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream and a 184-byte TS payload for storing data. ThePES packets are divided, and stored in the TS payloads, respectively.When a BD ROM is used, each of the TS packets is given a 4-byteTP_Extra_Header, thus resulting in 192-byte source packets. The sourcepackets are written on the multiplexed data. The TP_Extra_Header storesinformation such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The source packets are arranged in the multiplexed dataas shown at the bottom of FIG. 32. The numbers incrementing from thehead of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 33 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 34. The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 34, the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 35, a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of astream type included in the PMT. Furthermore, when the multiplexed datais recorded on a recording medium, the video stream attributeinformation included in the multiplexed data information is used. Morespecifically, the moving picture coding method or the moving picturecoding apparatus described in each of embodiments includes a step or aunit for allocating unique information indicating video data generatedby the moving picture coding method or the moving picture codingapparatus in each of embodiments, to the stream type included in the PMTor the video stream attribute information. With the configuration, thevideo data generated by the moving picture coding method or the movingpicture coding apparatus described in each of embodiments can bedistinguished from video data that conforms to another standard.

Furthermore, FIG. 36 illustrates steps of the moving picture decodingmethod according to the present embodiment. In Step exS100, the streamtype included in the PMT or the video stream attribute informationincluded in the multiplexed data information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the moving picture coding method orthe moving picture coding apparatus in each of embodiments. When it isdetermined that the stream type or the video stream attributeinformation indicates that the multiplexed data is generated by themoving picture coding method or the moving picture coding apparatus ineach of embodiments, in Step exS102, decoding is performed by the movingpicture decoding method in each of embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG-4 AVC,and VC-1, in Step exS103, decoding is performed by a moving picturedecoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not themoving picture decoding method or the moving picture decoding apparatusthat is described in each of embodiments can perform decoding. Even whenmultiplexed data that conforms to a different standard is input, anappropriate decoding method or apparatus can be selected. Thus, itbecomes possible to decode information without any error. Furthermore,the moving picture coding method or apparatus, or the moving picturedecoding method or apparatus in the present embodiment can be used inthe devices and systems described above.

Embodiment 9

Each of the moving picture coding method, the moving picture codingapparatus, the moving picture decoding method, and the moving picturedecoding apparatus in each of embodiments is typically achieved in theform of an integrated circuit or a Large Scale Integrated (LSI) circuit.As an example of the LSI, FIG. 37 illustrates a configuration of the LSIex500 that is made into one chip. The LSI ex500 includes elements ex501,ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to bedescribed below, and the elements are connected to each other through abus ex510. The power supply circuit unit ex505 is activated by supplyingeach of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recordingmedium ex215. When data sets are multiplexed, the data should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other.

Although the memory ex511 is an element outside the LSI ex500, it may beincluded in the LSI ex500. The buffer ex508 is not limited to onebuffer, but may be composed of buffers. Furthermore, the LSI ex500 maybe made into one chip or a plurality of chips.

Furthermore, although the control unit ex501 includes the CPU ex502, thememory controller ex503, the stream controller ex504, the drivingfrequency control unit ex512, the configuration of the control unitex501 is not limited to such. For example, the signal processing unitex507 may further include a CPU. Inclusion of another CPU in the signalprocessing unit ex507 can improve the processing speed. Furthermore, asanother example, the CPU ex502 may serve as or be a part of the signalprocessing unit ex507, and, for example, may include an audio signalprocessing unit. In such a case, the control unit ex501 includes thesignal processing unit ex507 or the CPU ex502 including a part of thesignal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present inventionis applied to biotechnology.

Embodiment 10

When video data generated in the moving picture coding method or by themoving picture coding apparatus described in each of embodiments isdecoded, compared to when video data that conforms to a conventionalstandard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, theprocessing amount probably increases. Thus, the LSI ex500 needs to beset to a driving frequency higher than that of the CPU ex502 to be usedwhen video data in conformity with the conventional standard is decoded.However, when the driving frequency is set higher, there is a problemthat the power consumption increases.

In order to solve the problem, the moving picture decoding apparatus,such as the television ex300 and the LSI ex500 is configured todetermine to which standard the video data conforms, and switch betweenthe driving frequencies according to the determined standard. FIG. 38illustrates a configuration ex800 in the present embodiment. A drivingfrequency switching unit ex803 sets a driving frequency to a higherdriving frequency when video data is generated by the moving picturecoding method or the moving picture coding apparatus described in eachof embodiments. Then, the driving frequency switching unit ex803instructs a decoding processing unit ex801 that executes the movingpicture decoding method described in each of embodiments to decode thevideo data. When the video data conforms to the conventional standard,the driving frequency switching unit ex803 sets a driving frequency to alower driving frequency than that of the video data generated by themoving picture coding method or the moving picture coding apparatusdescribed in each of embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 37.Here, each of the decoding processing unit ex801 that executes themoving picture decoding method described in each of embodiments and thedecoding processing unit ex802 that conforms to the conventionalstandard corresponds to the signal processing unit ex507 in FIG. 37. TheCPU ex502 determines to which standard the video data conforms. Then,the driving frequency control unit ex512 determines a driving frequencybased on a signal from the CPU ex502. Furthermore, the signal processingunit ex507 decodes the video data based on the signal from the CPUex502. For example, the identification information described inEmbodiment 8 is probably used for identifying the video data. Theidentification information is not limited to the one described inEmbodiment 8 but may be any information as long as the informationindicates to which standard the video data conforms. For example, whenwhich standard video data conforms to can be determined based on anexternal signal for determining that the video data is used for atelevision or a disk, etc., the determination may be made based on suchan external signal. Furthermore, the CPU ex502 selects a drivingfrequency based on, for example, a look-up table in which the standardsof the video data are associated with the driving frequencies as shownin FIG. 40. The driving frequency can be selected by storing the look-uptable in the buffer ex508 and in an internal memory of an LSI, and withreference to the look-up table by the CPU ex502.

FIG. 39 illustrates steps for executing a method in the presentembodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, inStep exS201, the CPU ex502 determines whether or not the video data isgenerated by the coding method and the coding apparatus described ineach of embodiments, based on the identification information. When thevideo data is generated by the moving picture coding method and themoving picture coding apparatus described in each of embodiments, inStep exS202, the CPU ex502 transmits a signal for setting the drivingfrequency to a higher driving frequency to the driving frequency controlunit ex512. Then, the driving frequency control unit ex512 sets thedriving frequency to the higher driving frequency. On the other hand,when the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1, in Step exS203, the CPU ex502 transmits a signal for setting thedriving frequency to a lower driving frequency to the driving frequencycontrol unit ex512. Then, the driving frequency control unit ex512 setsthe driving frequency to the lower driving frequency than that in thecase where the video data is generated by the moving picture codingmethod and the moving picture coding apparatus described in each ofembodiment.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the processing amount for decoding is larger, thedriving frequency may be set higher, and when the processing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when theprocessing amount for decoding video data in conformity with MPEG-4 AVCis larger than the processing amount for decoding video data generatedby the moving picture coding method and the moving picture codingapparatus described in each of embodiments, the driving frequency isprobably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the moving picture coding method and the moving picturecoding apparatus described in each of embodiments, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set higher. When the identification information indicates thatthe video data conforms to the conventional standard, such as MPEG-2,MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500 or theapparatus including the LSI ex500 is probably set lower. As anotherexample, when the identification information indicates that the videodata is generated by the moving picture coding method and the movingpicture coding apparatus described in each of embodiments, the drivingof the CPU ex502 does not probably have to be suspended. When theidentification information indicates that the video data conforms to theconventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the drivingof the CPU ex502 is probably suspended at a given time because the CPUex502 has extra processing capacity. Even when the identificationinformation indicates that the video data is generated by the movingpicture coding method and the moving picture coding apparatus describedin each of embodiments, in the case where the CPU ex502 has extraprocessing capacity, the driving of the CPU ex502 is probably suspendedat a given time. In such a case, the suspending time is probably setshorter than that in the case where when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment 11

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, the problems of increase in the scale ofthe circuit of the LSI ex500 and increase in the cost arise with theindividual use of the signal processing units ex507 that conform to therespective standards.

In order to solve the problem, what is conceived is a configuration inwhich the decoding processing unit for implementing the moving picturedecoding method described in each of embodiments and the decodingprocessing unit that conforms to the conventional standard, such asMPEG-2, MPEG-4 AVC, and VC-1 are partly shared. Ex900 in FIG. 41A showsan example of the configuration. For example, the moving picturedecoding method described in each of embodiments and the moving picturedecoding method that conforms to MPEG-4 AVC have, partly in common, thedetails of processing, such as entropy coding, inverse quantization,deblocking filtering, and motion compensated prediction. The details ofprocessing to be shared probably include use of a decoding processingunit ex902 that conforms to MPEG-4 AVC. In contrast, a dedicateddecoding processing unit ex901 is probably used for other processingunique to an aspect of the present invention. Since the aspect of thepresent invention is characterized by inverse quantization inparticular, for example, the dedicated decoding processing unit ex901 isused for inverse quantization. Otherwise, the decoding processing unitis probably shared for one of the entropy decoding, deblockingfiltering, and motion compensation, or all of the processing. Thedecoding processing unit for implementing the moving picture decodingmethod described in each of embodiments may be shared for the processingto be shared, and a dedicated decoding processing unit may be used forprocessing unique to that of MPEG-4 AVC.

Furthermore, ex1000 in FIG. 41B shows another example in that processingis partly shared. This example uses a configuration including adedicated decoding processing unit ex1001 that supports the processingunique to an aspect of the present invention, a dedicated decodingprocessing unit ex1002 that supports the processing unique to anotherconventional standard, and a decoding processing unit ex1003 thatsupports processing to be shared between the moving picture decodingmethod according to the aspect of the present invention and theconventional moving picture decoding method. Here, the dedicateddecoding processing units ex1001 and ex1002 are not necessarilyspecialized for the processing according to the aspect of the presentinvention and the processing of the conventional standard, respectively,and may be the ones capable of implementing general processing.Furthermore, the configuration of the present embodiment can beimplemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the moving picture decoding methodaccording to the aspect of the present invention and the moving picturedecoding method in conformity with the conventional standard.

INDUSTRIAL APPLICABILITY

The image coding method and the image decoding method according to thepresent invention can be used for various purposes. For example, thepresent invention can be used for a high-resolution image displayapparatus and a high-resolution image pickup apparatus, such as atelevision, a digital video recorder, a car navigation system, acellular phone, a digital camera, and a digital video camera.

REFERENCE SIGNS LIST

-   100, 300 Chroma-signal intra prediction unit-   110, 330, 510, 610, 710, 830, 940, 1030 Intra-predicted    chroma-signal generation unit-   120, 520, 620, 720 Residual signal calculation unit-   130, 210, 530, 630, 730 Transform-quantization unit-   135, 230, 535, 635, 735 Inverse quantization-transform unit-   140 Coded-signal generation unit-   150, 570, 670, 770 Coding unit-   200 Image coding apparatus-   205 Subtracter-   220 Entropy coding unit-   235, 425 Adder-   240, 430 Deblocking filter-   250, 440 Memory-   260, 450 Intra prediction unit-   270 Motion estimation unit-   280, 460 Motion compensation unit-   290, 470 Intra/inter selection switch-   310, 810, 910, 1010 Variable-length decoding unit-   320, 820, 920, 1020 Residual signal obtainment unit-   340 Decoded-chroma-signal generation unit-   400 Image decoding apparatus-   410 Entropy decoding unit-   500, 600, 700, 800, 900, 1000 Image processing apparatus-   540, 640, 740 temporary coded chroma-signal generation unit-   550, 650, 750 First DC component calculation unit-   555, 655, 755 Second DC component calculation unit-   560, 660, 760 Offset value calculation unit-   580, 680, 780, 850, 950, 1060 Offset value addition unit-   690, 960 Offsetting determination unit-   790 Unit-of-offsetting determination unit-   840, 930, 1040 Temporary decoded chroma-signal generation unit-   1070 Unit-of-offsetting information obtainment unit

1. An image coding method of coding an input block included in an image,the image coding method comprising: generating a predicted block bypredicting the input block; calculating a residual block by subtractingthe predicted block from the input block; calculating quantizedcoefficients by performing transform and quantization on the residualblock; calculating a coded residual block by performing inversequantization and inverse transform on the quantized coefficients;generating a temporary coded block by adding the coded residual block tothe predicted block; determining whether or not an offset process forcorrecting an error included in a chroma block included in the temporarycoded block is required, to generate first information indicating aresult of the determination, the error being caused by the quantizationin the calculating of quantized coefficients; executing the offsetprocess on the chroma block when it is determined in the determiningthat the offset process is required; and performing variable-lengthcoding on the quantized coefficients and the first information.
 2. Animage coding method of coding an input block included in an image, theimage coding method comprising: generating a predicted block bypredicting the input block; calculating a residual block by subtractingthe predicted block from the input block; calculating quantizedcoefficients by performing transform and quantization on the residualblock; calculating a coded residual block by performing inversequantization and inverse transform on the quantized coefficients;generating a temporary coded block by adding the coded residual block tothe predicted block; determining whether or not an offset process forcorrecting an error included in a luma block included in the temporarycoded block is required, to generate second information indicating aresult of the determination, the error being caused by the quantizationin the calculating of quantized coefficients; executing the offsetprocess on the luma block when it is determined in the determining thatthe offset process is required; and performing variable-length coding onthe quantized coefficients and the second information.
 3. An imagecoding method of coding an input block included in an image, the imagecoding method comprising: generating a predicted block by predicting theinput block; calculating a residual block by subtracting the predictedblock from the input block; calculating quantized coefficients byperforming transform and quantization on the residual block; calculatinga coded residual block by performing inverse quantization and inversetransform on the quantized coefficients; generating a temporary codedblock by adding the coded residual block to the predicted block;determining whether or not an offset process for correcting an errorincluded in a chroma block included in the temporary coded block isrequired, to generate first information indicating a result of thedetermination for the chroma block, the error being caused by thequantization in the calculating of quantized coefficients; determiningwhether or not an offset process for correcting an error included in aluma block included in the temporary coded block is required, togenerate second information indicating a result of the determination forthe luma block, the error being caused by the quantization in thecalculating of quantized coefficients; executing the offset process onthe chroma block when it is determined that the offset process for thechroma block is required; executing the offset process on the luma blockwhen it is determined that the offset process for the luma block isrequired; and performing variable-length coding on the quantizedcoefficients, the first information and the second information.
 4. Animage coding apparatus that codes an input block included in an image,the image coding apparatus comprising: a prediction unit configured togenerate a predicted block by predicting the input block; a calculationunit configured to calculate a residual block by subtracting thepredicted block from the input block; a transform-quantization unitconfigured to calculate quantized coefficients by performing transformand quantization on the residual block; an inversequantization-transform unit configured to calculate a coded residualblock by performing inverse quantization and inverse transform on thequantized coefficients; a generation unit configured to generate atemporary coded block by adding the coded residual block to thepredicted block; a determination unit configured to determine whether ornot an offset process for correcting an error included in a chroma blockincluded in the temporary coded block is required, to generate firstinformation indicating a result of the determination, the error beingcaused by the quantization performed by the transform-quantization unit;an offset processing unit configured to execute the offset process onthe chroma block when it is determined by the determination unit thatthe offset process is required; and a variable-length coding unitconfigured to perform variable-length coding on the quantizedcoefficients and the first information.
 5. An image coding apparatusthat codes an input block included in an image, the image codingapparatus comprising: a prediction unit configured to generate apredicted block by predicting the input block; a calculation unitconfigured to calculate a residual block by subtracting the predictedblock from the input block; a transform-quantization unit configured tocalculate quantized coefficients by performing transform andquantization on the residual block; an inverse quantization-transformunit configured to calculate a coded residual block by performinginverse quantization and inverse transform on the quantizedcoefficients; a generation unit configured to generate a temporary codedblock by adding the coded residual block to the predicted block; adetermination unit configured to determine whether or not an offsetprocess for correcting an error included in a luma block included in thetemporary coded block is required, to generate second informationindicating a result of the determination, the error being caused by thequantization performed by the transform-quantization unit; an offsetprocessing unit configured to execute the offset process on the lumablock when it is determined by the determination unit that the offsetprocess is required; and a variable-length coding unit configured toperform variable-length coding on the quantized coefficients and thesecond information.
 6. An image coding apparatus that codes an inputblock included in an image, the image coding apparatus comprising: aprediction unit configured to generate a predicted block by predictingthe input block; a calculation unit configured to calculate a residualblock by subtracting the predicted block from the input block; atransform-quantization unit configured to calculate quantizedcoefficients by performing transform and quantization on the residualblock; an inverse quantization-transform unit configured to calculate acoded residual block by performing inverse quantization and inversetransform on the quantized coefficients; a generation unit configured togenerate a temporary coded block by adding the coded residual block tothe predicted block; a first determination unit configured to determinewhether or not an offset process for correcting an error included in achroma block included in the temporary coded block is required, togenerate first information indicating a result of the determination forthe chroma block, the error being caused by the quantization performedby the transform-quantization unit; a second determination unitconfigured to determine whether or not an offset process for correctingan error included in a luma block included in the temporary coded blockis required, to generate second information indicating a result of thedetermination for the luma block, the error being caused by thequantization performed by the transform-quantization unit; a firstoffset processing unit configured to execute the offset process on thechroma block when it is determined by the first determination unit thatthe offset process for the chroma block is required; a second offsetprocessing unit configured to execute the offset process on the lumablock when it is determined by the second determination unit that theoffset process for the luma block is required; and a variable-lengthcoding unit configured to perform variable-length coding on thequantized coefficients, the first information and the secondinformation.